Dewatering, waterproofing and drainage - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 195

Table 5-10 Methods of water collection [251].

Point collection Linear collection Surface collection

- Drilling,
- Push-fit pipes
- Drip channel

- Oberhasli process (purely manual,
outdated)
- Filter pipes (holed with filter sur-
round)
- Semi-circular channel drainage
(much manual work, blockage
through pointing)
- Filter strips
- dimpled sheeting or ribbed foil
- drainage mats
- structured mats

- No-fines outer support layer (ela-
borate tunnel construction method
from the 1960s)
- No-fines concrete fill instead of con-
struction material sluicing, possible
with multi-layer tunnel lining
- U-profile precast element drainage
- Dimpled drainage sheets, ribbed
drainage foil and structured mats
- Protective fleece as drainage and
protection element for foil water-
proofing membrane
- Invert filter according to the type of
frost protection layer

The most important processes are described in the following section.

Plastic gutters and channels with various profiles (Fig. 5-4) are used to collect localised
water ingress. Gutters made of soft PVC and stiffened longwise and crosswise with steel
wire are laid by hand with rapid-hardening cement mortar or temporarily fixed with forked
pins until they have been covered with a shotcrete layer a few centimetres thick.

Form U: 66/108 mm wide semi-circular
section with 19 cm 2 flow section; roll:
25 m, 240 g/m

Figure 5-4 Drainage channel of plastic; Aliva AG.

Protective fleece. The main purpose of the fleeces that are normally provided between
temporary support and final lining is the protection of the waterproofing membrane
against mechanical damage, for example perforation due to the rough surface of the shot-
crete substrate. Protective fleeces should also enable surface collection and drainage of
groundwater. In order to ensure that this function is effective, qualitative and as far as pos-
sible quantitative verifications should be undertaken of the flow quantities and measures
to avoid sintering.
Drainage or dimpled mats. Drainage mats of plastic (Fig. 5-5) are used when large quan-
tities of groundwater are expected to appear from large areas. The dimpled side should
ideally be installed to the outside - against the rock. Since the application of shotcrete onto
the dimpled sheet is impractical, they are often laid on the shotcrete support layer and an
in-situ concrete inner lining is then concreted, with or without waterproofing.